HS2 keep on changing their plans for train size, are they are all to be British size or a mixture of UIC (European) size and British size? UIC size is about 45cm wider, not enough to fit in another seat, but enough to make 2+2 seating more comfortable, and enough to require special arrangements for fitting both widths into the same platform. "Special arrangements" is rather an exaggeration, as this picture shows. it.

A station in Germany for both trams and trains. The left-hand platform takes only trams. The right-hand platform takes both trams and mainline trains. The 1st and 3rd rails from the platform edge are for trams, which are narrower, and the 2nd and 4th rails are for wider mainline trains. All are standard gauge.

Trains of different sizes will simply be switched onto different rails. London Transport have run two sizes of train for over 100 years and have not yet sent a bigger train into a smaller tunnel. It will always be possible to run narrower trains on wider routes.

Taller is also possible; 3+3 seating on double decks would be possible on channel tunnel shuttle trains, which can carry full-size road vehicle. These were the biggest in the world, but they are now equalled in height by

Trains are getting bigger, like most things, the freight-only Betuwe route (between Rotterdam and Germany) is built to carry stacked containers and the Gotthard base tunnel has been built to carry full-size road vehicles, and so have our own Channel Tunnel Shuttles.

Channel Tunnel shuttle trains are 4.10 Metres wide and 5.57 Metres high. The Channel tunnel bores are 7.60 Metres in diameter to fit and the bores of the CTRL are 7.15 Metres in diameter, so trains of this size can be run London – France. Energy use is proportional to surface area and a simple calculation shows what energy saving this allows.Description* Height M Width M Seats/Slice Circumference/seats ratioCurrent British standard 4..0 2.8 4 13.6/ 4 = 3.4Channel tunnel size. 5.57 4.10 12 19.34/12 = 1.61

The surface area/seats ratio has been halved and with it energy/seat-km. This cuts energy costs, but prices are such that the commercial advantage is small *The Japanese Shinkansen has 3+2 seating in coaches 3.4 M wide. The Boeing 737 and Airbus A320 aircraft seat 3 + 3 in bodies 3.7 M wide. The Channel tunnel size is even wider, giving more elbow room and gangway width.

Traditionally British and other European railway trains have been about 200 Metres long. French railways have coupled some of their trains nose to tail and created trains of 400 metres long and UIC have latched onto this and declared it a European norm, but there is no need to go so far. HS2 have adopted this standard, but it creates needless difficulties in a British setting. A 200 M long train seating 3+3 on two decks can carry 1.5 as many people as one of HS2’s 400 Metre long trains seating 2+2 on one deck. That’s an increase in capacity which could hardly be got in any other way. It also allows bigger doors and therefore easier boarding.

This trend to bigness is universal and is more likely to be continued than reversed. The Gotthard base tunnel is being fitted out to take whole road-going vehicles, and allowance has been made for much bigger. The freight-only Betuwelijn/Hollandstrecke between Rotterdam and Germany has been built to take double-stacked containers.

Aircraft speeds have settled at 560 mph, and railway top speeds seem likely to settle at 250- 300 mph, about half aircraft speeds, with much lower emissions and costs. The airlines have invented ways of allowing passenger to sleep, and similar arrangements on trains would allow rail to compete within Europe and maybe over long distances, . Meanwhile goods transport and tourism grow apace and long-distance railway lines are likely to be built, Europe – China, Europe - India, Europe – Africa.

I once heard a Parliamentary debate in which a speaker said, in the snootiest possible voice, “There is no need to extend this feature (I’ve forgotten what it was) beyond London”. There would be great anger if a break of loading gauge were to be built at London.Fitting in bigger trains.

It might seem that it will be much more expensive to build a route for a bigger train than for a smaller one.But take that to its logical limit; if you built the route to the standards of curvature and gradient which are needed for trains of this speed, but cut the size down to that needed to lay a piano wire, how much cost would you cut out? Think about it!Answer; very little!

When necessary oversize trains will fit onto existing routes Look at this picture of a train coming under a bridge near Newcastle.

The bridge would have to be raised, but the boundary fences are far enough apart to allow trains 4.1 M wide rather than this pair of 2.8 M wide tracks.There is no problem with roof height in main stations; most of them have roof height which far exceeds the needs. Cutting back the platform edges is not a problem.

There’s a hidden cost to long trains; people prefer to walk at about 1.4 M/sec, over 400 M that amounts to 4 mins 45 seconds, and there will always be some laggards. This creates problems of platform management, it has to be taken into account for connections and it is part of total journey time.

The main problem with 400 Metre long trains is that they need stations of that length, and more if they are terminus stations. Few British city centre sites could allow that, it breaks up street patterns. Newcastle central is one of the few that could allow 400 M long trains, and that is only because the space that used to be used by the 3rd rail electric trains at the east end of the station is now empty and the line that used to parallel Scotswood Road at the west end has been abandoned and trains could now lie round the curve. Look at it and imagine how it would fit into a town you know. Newcastle is nearly unique; in most other cities, trains of 400 Metres long would require stations extending far into very expensive and valuable city centre space.